Opposition parties have been closing in on an impeachment motion against her and even her allies in the conservative ruling party have called for her to step down "honourably" rather than face impeachment.

Ms Park previously rejected calls to leave office and dismissed prosecutors' claim that she colluded with a confidante who allegedly manipulated power from the shadows and extorted companies to amass an illicit fortune.

AP

Hundreds of thousands have gathered in Seoul each Saturday for the last five weeks to demand that Ms Park step down.

She would be the first South Korean leader to resign since the country's first president, Syngman Rhee, quit, then fled to Hawaii amid a popular uprising in 1960.

The succeeding government was overthrown by a coup by Ms Park's late father, the military dictator Park Chung-hee, whose rule also abruptly ended after he was assassinated by his spy chief in 1979.

"I will leave the matters about my fate, including the shortening of my presidential term, to be decided by the National Assembly," Ms Park said in a live address to the nation, referring to parliament.

"If the ruling and opposition parties discuss and come up with a plan to reduce the confusion in state affairs and ensure a safe transfer of governments, I will resign from the presidential position under that schedule and by processes stated in law."

An impeachment vote had been planned for Friday and the country's two largest opposition parties were also planning on Tuesday to nominate a special prosecutor to independently investigate the scandal.

At the heart of the scandal is Choi Soon-sil, Ms Park's long-time friend and the daughter of a late cult leader who allegedly meddled in state affairs and pressured companies to donate millions of dollars to foundations controlled by her at the request of Ms Park.

Prosecutors have so far indicted Ms Choi, two ex-presidential officials and a music video director known as a Choi associate for extortion, leakage of confidential documents and other charges.

Ms Park, who has immunity from prosecution while in office, has refused to meet prosecutors and her lawyer, Yoo Yeong-ha, has described prosecutors' accusations as groundless.

The country's largest opposition group, the Minjoo Party, called Ms Park's address a ploy to avoid an impeachment vote and said it would continue to push for impeachment as planned.